As pointed by business week(via trak.in), the innovations made by Tata Nano are:

   1. The car was built from ground up.
   2. The supply chain was simplified by making the suppliers partners.
   3. Shipping the whole car as kits for the downstream distributors to assemble, thus reducing several costs.
   4. The key success factor for Tata Nano project was price. The price was fixed and everything else just worked around it.

Agreed, regulations are less stringent in India. However, price is an innovation. I can argue that a retrofitted Tata Nano will cost no more then $5000 for US market. So, there is ample room for innovation.